Process of dedusting soap and the resulting product



Patented Apr. 15, 1952 PROCESS OF DEDUSTING SOAP AND THE RESULTING PRODUCT John W. Badman, Winchester, Mass., assignor to Lever Brothers Company, Cambridge, Mass., a

corporation of Maine No Drawing. Application July 20, 1948, Serial No. 39,806. In Great Britain August 1, 1941 7 Claims.

This invention relates to improvements in the manufacture of soaps and more particularly to powdered, granulated or comminuted soaps substantially devoid of objectionable finely divided soap dust particles; the invention relates also to methods of manufacturing such soaps.

Granulated or powdered soaps usually are formed in one of three well-known ways, namely, grinding, in which dried soap is comminuted and reduced to a powdered condition; spraycooling, wherein a hot liquid soap that is capable of crystallizing is sprayed into a current of cooling air; and spray-drying, wherein a hot liquid or semi-liquid soap or soap mix is sprayed into a current of heated drying gas to evaporate a portion of the water and cause the soap to solidify as particles, or wherein soap is heated under pressure and flashed into cool air at lower pressure. Spray dried soaps may be either hollow or porous fragile particles.

Soaps of these types are usually packaged in cardboard cartons and are sold to the consuming public in this convenient form. While such soaps are highly desirable from the standpoint of ease in solubility and convenience in use, when they reach the consumer they contain a quantity of finely divided soap particles. A material proportion of this dust or fines is capable of being air borne. The portion of the dust capable of being air borne is usually released upon opening the carton and pouring the soap therefrom. It is this air borne soap dust that has been found in many cases to irritate the membranes of the nose and throat, causing coughing and sneezing.

The dust particles or fines also have a tendency to lump together on the surface of the water and resist solution. This characteristic of comminuted or powdered soap products has long been recognized in the industry and attempts have been made to eliminate the dust or at least materially reduce the quantity in the product.

Theattempts to overcome this difficulty have led to improvements in spray-drying processes, by means of which the soap is formed into more or less rounded and discrete individual granules. Such granules are small enough to dissolve readily, but also large enough to minimize greatly the disadvantages of the so-called dusting. The factors affecting the size and character of the soap granules produced in a spray-drying process are well known. For example, fine particles can be pufied to above dust size if high temperatures and otherv conditions are employed. However, large puffing generally is not desirable, for in doing this to the fine particles, the total product 7 is bulked to such a large degree that in general there is present too small an amount of soap in any given volume, and the product does not have desirable sudsing properties. Furthermore, large puffing creates thin walled particles more susceptible to breakage, thus tending to increase the dust content of the product.

In spite of the exact control now possible, there is still generally an objectionable amount of dusty material in the product at the time the customer uses it. A proportion of fines unavoidably results from the commercial manufacturing processes. Dust formed during the process of manufacture could be made relatively unobjectionable in the final product by an emcient dedusting process after manufacture and prior to packaging. One of the principal causes of dust in the packaged product is the disintegration of the particles after the product is packaged. This may be because of conditions of storing and handling before or after the carton or package is opened for use.

Attempts to remove finely divided material of dust size by screening before packaging have not been successful, however, for the reason that screens of sufficient fineness to allow separation of the dust become clogged, and, at best, remove only a part of the dust. Even assuming that. a

screening process removes the dust formed during the production of the soap, it cannot remove the dust which is formed in the package.

The formation of dust in the package results, in part, from disintegration of the soap particles during handling and is increased by drying out of the soap. A soap product such as, for example, a spray-dried soap, may consist of more or less spherical globules, each having one or more voids therein. A moisture content of between 10 percent to 20 percent is normally present in typical forms of granulated soaps at the time they are. manufactured and packaged. This moisture content is sufiicient to render the particles somewhat plastic and resistant to shattering. As long as this moisture content is maintained at substantially its initial amount, there is little tendency for the soap to form dust, How-, ever, if the soap dries, as is often the case, the plasticity of the particles is then reduced. Upon being subjected to shock or abrasion, the dried and friable particles will break or shatter and thus form additional quantities of dust. Low moisture content also impedes any tendency towards a reaggregation of the fines into largeragglomerates. In additionrloss of moisturepermits a migration of fillers orbuilders in the soap,

such as sodium carbonate, sodium sulfate and sodium silicate, toward the surfaces of the particles where they deposit as crust or g p of crystals. These crystals are separable by abrasion from the larger particles as dust. In the case of the more alkaline fillers, such as sodium carbonate or sodium silicate, this form of dust is of a particularly irritating nature. There is also a tendency for the dust to remain in suspension in the air because of the presence of static charges of like sign on the particles. Such electrical dispersing charges may be created as a result of friction between the particles and the package during handling. The presence of adequate moisture content in the particles, however, largely eliminates the effects. of static electricity.

The breaking up or disintegration of the soap particles also has the undesirable efiect of reducing the apparent volume of the soap in the cartons. This creates an adverse psychological elfect'upon the user when the package of soap is opened, inasmuch as it would appear as if less than the full quantity of soap were present in the. package.

It has been suggested that drying out of the soap particles might be avoided by packaging the granulated soap in moisture-proof containers. While this increases the cost of packaging, it will, of course, prevent drying of the soap as long as the package is unopened, but inasmuch as the entire contents of the soap package ordinarily is not used immediately after opening the package, the remainder of thesoap will dry out readily upon standing in a dry place, and objectionable dust will be formed.

My invention may be utilized to overcome and avoid at least some, and preferably all, of the disadvantages and dificulties of the type indicated above, as well as others, in comminuted friable substances, and for preserving and improving such substances, particularly those of the type of soap. In this connection the invention may preferably be utilized to substantially reduce the tendency of granulated or powdered soaps or other such friable substances to disintegrate or change their physical state with consequent dust formation. The invention may also be preferably utilized to maintain the moisture content of soap particles substantially constant despite variations in relative humidity so as to minimize and prevent the drying out of the soap particles with a resultant undesirable formation of dust. The invention may be utilized to minimize or eliminate dust particles present in a soap product, for example, by maintaining the soap in an undried form so as to retain the strength of the soap particles; consequently there is little or no tendency for the soap particles to disintegrate or change their state. Under some circumstances the surface of the larger particles may hold the fines attached thereto or the fines may be held together through a cohesive action.

I have subsequently set forth preferred examples and illustrations of how my process may preferably be practiced to produce desirable products. 7 r

In accordance with the present invention the individual soap particles or granules, afterthey are formed, may be coated with a. material that functions primarily because of its hygroscopic nature and whichnormally withdraws moisture from the atmosphere and thus prevents a'migration Qrdifiusion of the moisture from the interior of thesoap particles. .Th hygroscopic material in many cases also may act to bind dust particles to each other or to the larger particles. These dust particles may be present in the soap initially or may be formed if the soap is subject to unusual conditions.

Of the materials which have been used in treating granulated soap, the organic and inorganic phosphates, such as, for example, disodium phosphate, dipotassium phosphate or potassium methyl or ethyl phosphate, are satisfactory hygroscopic coating materials. Dipotassium phosphate is very efiective at relative humidities in excessrof about 30 percent. For example at 50 percent relative humidity, dipotassium phosphate will carry about 40 percent of water, which is adequate to maintain it in the form of an oily or mobile liquid. However, below about 30 percent relative humidity, it will dry out to a crystalline solid. Therefore, it is less suitable for use in treating soap which will be exposed to very low humidities. The presence of an alkyl group, such as an ethyl or methyl group, in place of one of the alkali metal ions, results in compounds which will retain their fluidity at extremely low humidities. Alkyl phosphates, having the formula MRI-IP04, in which M is any cation such as alkali metal and R is any alkyl group, as long as the compound is water soluble, are particularly suitable for use as coating agents for granulated soap under all conditions of relative humidity.

The above mentioned compounds also cause any dust particles to aggregate into larger particles or adhere to large soap granules. They also minimize the formation of static charges and thus reduce the tendency of any small soap particles to remain in suspension. These hygroscopic materials function as wetting agents and contribute to the plasticity of the soap particles because of their wetting nature and strengthen the bond between aggregates of fines and between the fines and the particles of normal size.

Hygroscopic substances or those which themselves may be conductors have the additional characteristic of preventing the formation of static charges on the soap particles for the reason that they render the surfaces of the particles conductive, and thus reduce the tendency of the dust to remain in suspension in air. Such substances which might be used for this purpose would include, for example, dipotassium phosphate, sodium potassium ethyl phosphate, triethanolamine ethyl phosphate, glycerin and dipotassium phosphate, and glycerin and sodium potassium ethyl phosphate.

The various materials mentioned may be used alone or in any admixture.

These coating compositions should be present in sufficient proportion to obtain the desired results and yet not in such proportion that they will cause lumping and formation of aggregates of such size that the characteristic of rapid dissolving, which is desirable in granulated soaps, is materially reduced.

It is desirable to prevent excess quantities of the coating material from impinging upon the soap particles in order to prevent them from sticking or lumping together and interfering with their normally free-flowing properties. Since the coating material is applied only to the surface of the particles, very small quantities are required. This makes the process particularly economical andachieves results that would be prohibitive from the standpoint of cost if the material were incorporated within the soap-before it was placed'in granular form.

' The amount of the hygroscopic material to be employed will depend upon the hygroscopic character of the material selected, the nature of the soap, the climatic conditions where the product is to be used, etc. Soaps made from certain fatty acids and alkalies and having certain fillers and builders have different degreesofnatural plasticities and Water retentivity. This fact coupled with the different hygroscopic character of various materials makes it difiicult to state any range applicable to all of the hygroscopic materials: In general the range is A; to 5%. For example, 100 pounds of spray dried soap may be treated with 2 pounds of dipotassium phosphate dissolved in two pounds of water. It is believed thatin view of the generic disclosure and the specific example, one skilled in the art would readily be-able to determine the amount to be used in any particular instance. depending upon the particular soap to be treated and the use to which it is to be put.

It will be understood that a greater or less amount of the coating composition referred to may be used, depending on the character and physical characteristics of the granulated soap treated. Greater amounts of these coating compositions may be used, although this increases the cost of treating the soap.

It is characteristic of the invention that the hygroscopic material is applied to the surface of the particles as distinguished from an ingredient that is admixed with the soap composition before it is dried. In the latter case, the hygroscopic material would not have an opportunity to exert its hygroscopic character to any marked extent. As the soap particle dries, the moisture first leaves the outer surface and it is the outer surface which dries first. The moisture from the interior then migrates through the particle to the outer surface. Thus if the outer surface can be kept moist as a result of the hygroscopic material, there will be no tendency for the normal moisture on the interior to leave the particles. Furthermore, since it is only the surface of the particle which is in contact with the air from which moisture could be absorbed by hygroscopicity, there is no point in having the hygroscopic material at any point other than on the outside surface of the soap particles. The hygroscopic material may be applied more or less uniformly over the surface of the soap particles and it may be applied more or less spotted or continuously over the surface.

Since the hygroscopic agents are water-soluble,

there is no objection to a continuous coating on the surface of the particles. although a partially spotted coating may be sufiicient to keep the soap particles plastic with the coating of this amount and nature.

The hygroscopic material is not soluble in the soap and has the advantage that it will not tend to difiuse into the soap particles.

The coating materials may be applied to soap particles in various ways, and at any convenient time between the formation of the soap particles and the packaging step. The coating materials are preferably atomized and the soap particles allowed to fall through the atomized coating material. It is desirable to maintain the finest possible mist or fog of the material to be applied so that the most effective application can be made and even the finest of the dust particles forced into contact with the treating material. It has been found that a series of repeating treatments is effective in obtaining a desirable dust-free product. Also, the coating composition may be applied by spraying in a rotary drum through which the soap particles are tumbled.

The major portion of the soap particles treated will, for the most part, vary in particle size from about 20'to80 mesh. They may be coated completely or partially with a single coating composition or a blend, simultaneously or in separate stages, as already described. Any fine, objectionable,'dust-like material will be coated and will tend to bond with the larger particles or with other fine material to form aggregates of a size larger than the average size of the dust particles. This will be the case not only with disintegrated or fine soap particles, but also with any dust formed as a result of the migration or separation of the ingredients ordinarily present in the soap composition, such as the hydrating salts. I

It has been found that in general dust-particles of a mesh of or smaller are undesirable in the final product and are considered as dust. It has been found that dust particles of about 400 mesh or smaller, as calculated on the bases of formulas for standard screens, will be air borne under conditions of relatively low air movement. These air borne particles might average 50 microns in size and smaller. They are, therefore, particularly undesirable as they can readily move into contact with the membrane of the nasal passages to cause irritation. Larger particles than 400 mesh may be air borne under conditions of increased air movement and for the same reason should be rendered innocuous.

From the foregoing it will be apparent that the present invention has resulted in the production of a novel dustless type of granular or comminuted soap product and that a simple process has been provided for obtaining such dustless soap granules. It will be understood that the present process can be applied to any of the usual types of granulated or powdered soaps in order to overcome their objectionable dusting characteristics and that by means of the process shrinkage in packaging or in weight may be largely avoided.

This application is a continuation-in-part of application Serial No. 494,847 filed July 15, 1943, now Patent No. 2,465,346, which in turn is a continuation-in-part of my pending application Serial No. 351,111 filed August 3, 1940, now Patent No. 2,329,694.

It will be understood that coating compositions similar to but other than those mentioned specifically above may be used without departing from the invention. Therefore. the forms of the invention described above should be considered as illustrative and not as limiting the scope of the following claims.

I claim:

1. A process for treating granulated watersoluble soap to reduce the amount of dust therein, comprising applying to at least a portion of the surface of the soap particles a hygroscopic phosphate for maintaining the soap particles in an undried plastic condition.

2. A process for treating granulated watersoluble soap to prevent substantially the formation of soap dust therein, comprising applying to soap particles a superficial coating of a hygroscopic phosphate for maintaining said particles plastic and resistant to shattering.

3. A process of treating water-soluble soap to prevent the formation of soap dust therein, comprising applying to the particles of soap a superficial coating of a normally liquid phosphate for wetting the particles and maintaining them plastic.

4. A process of treating water-soluble soap tov prevent the formation of soap dust therein, comprising. applying to the particles of soap a superficial coating of a normally liquid phosphate having the formula RMHPO4 in which R is an alkyl group and M is an alkali metal.

5. A process for treating granulated watersoluble soap to reduce the amount of dust therein, comprising spraying the surface of the Soap particles with a hygroscopic phosphate in liquid form for maintaining the soap particles in an undried and plastic condition.

-6. A water-soluble soap product comprising granulated soap particles having a moisture con tent sufficient to render them plastic and nondusting, and a superficial coating of a hygroscopic phosphate for preventing dehydration of said particles.

7. A water-soluble soap product comprising finely divided spray-dried soap particles having on at least a portion of their surfaces a superficial coating of an alkali metal alkyl phosphate.

JOHN W. BODMAN.

REFERENCES CITED The following references are of record in the file of this patent: 

7. A WATER-SOLUBLE SOAP PRODUCT COMPRISING FINELY DIVIDED SPRAY-DRIED SOAP PARTICLES HAVING ON AT LEAST A PORTION OF THEIR SURFACES A SUPERFICIAL COATING OF AN ALKALI METAL ALKYL PHOSPHATE. 